This invention relates to a sliding contact guide for a power transmission utilizing an endless, circulating, flexible power transmission medium. It relates, for example, to a guide in a chain drive transmission, in which a chain transmits power from a driving sprocket to a driven sprocket, or to a guide in a belt drive transmission, in which a belt transmits power from a driving pulley to a driven pulley.
In general, a chain or belt transmission device for valve timing in an internal combustion engine, or for transmitting rotational power in another drive mechanism, includes a pivotally mounted, movable sliding contact guide, which cooperates with a tensioner, and a fixed sliding contact guide. The movable guide and the fixed guide are attached to the body of the engine or other drive mechanism by bolts, pins, or similar mountings. The guides provide suitable tension by making sliding contact with the chain or belt, and also prevent vibrations of the chain or belt both in the plane of its traveling path (which is usually vertical), and in the transverse direction.
As shown in FIG. 6, a conventional movable sliding contact guide A (also referred to as a xe2x80x9ctensioner leverxe2x80x9d) is a two-piece structure comprising a shoe A10 composed of resin material for sliding contact with a chain, and also a die cast aluminum base member A20, the aluminum providing sufficient strength for holding and retaining the form of the shoe A10. This guide is the subject of Japanese Laid-open Patent Publication No. 346154/2000.
FIG. 7 shows another movable sliding contact guide or tensioner lever B, which takes the form of a two-piece structure comprising a shoe B10 composed of a resin material and a steel plate B20, which is required for strength and for holding and retaining the form of the shoe B10. This guide is the subject of Japanese Patent Application No. 69238/2001.
In the above-mentioned movable, sliding contact guides, various properties such as contact sliding properties, wear properties, mechanical strength and the like, are made compatible by selecting appropriate materials for the respective members of the two-piece structure, taking into account that the shoe requires good sliding properties and wear resistance, and the base or plate require good mechanical strength in order to retain the shoe.
Known movable type sliding contact guides are subject to several problems. The die cast aluminum base member A20 of the guide shown in FIG. 6, has relatively low strength. Thus, it needs to have a large volume and a large wall thickness to ensure rigidity. Accordingly this structure is not suitable for a guide in which weight reduction is desired. Moreover, material costs, and production costs, including molding costs, are high. Another problem is that assembly is troublesome, especially the operation by which hooks A11 are used to secure the base member A20 to the shoe A10. In the movable sliding contact guide B, as shown in FIG. 7, since the plate B20 is made of steel, in order to provide the strength required to hold the shoe B10, even if the plate is in the form of a thin sheet, the overall weight of the guide is relatively large, as in the case of the guide of FIG. 6, which utilizes a die cast aluminum base member.
Accordingly, the objects of the invention are to solve the above-mentioned problems encountered in prior art sliding contact guides, and to provide a sliding contact guide in which an overall weight reduction is achieved, and vibration noises, the energy of which increases with increasing weight, are suppressed.
In order to achieve the above objects, a sliding contact guide in accordance with the invention comprises an elongated shoe composed of synthetic resin. The shoe has front and back sides, and a surface extending longitudinally on the front side for sliding contact with an endless, circulating, flexible power transmission medium such as a chain or belt. An elongated plate-receiving portion, also composed of synthetic resin, integrally molded with the shoe on the back side, extends longitudinally along the back side of the shoe, and has a longitudinally extending slot. The slot has opposed walls disposed in perpendicular relation to said surface. A body mounting hole extends through the plate-receiving portion adjacent one end of the guide and intersects the slot. A reinforcing plate, for reinforcing the guide, fits in the slot and has opposite faces engaged respectively with the opposed walls of the slot. The plate also has a through hole in register with the body mounting hole. The guide is characterized by punched windows extending through the plate in the direction of its thickness, the windows being distributed along the length of the plate.
The synthetic resin forming the guide body in accordance with the invention is not particularly limited, but preferred materials are superior in wear resistance, and have lubricating properties suitable for a sliding shoe surface in contact with a chain, belt or the like. Suitable synthetic resins include, for example, nylon 6, nylon 66, nylon 46, all aromatic nylons and the like. So-called engineering plastics are preferably used, and, where superior strength is required, fiber-reinforced plastics are preferred.
The material of the reinforcing plate is likewise not particularly limited. However, non-ferrous metals such as aluminum, magnesium, titanium and the like, and engineering plastics, fiber-reinforcing plastics and the like, having improved bending rigidity and strength, are preferably used.
The windows punched in the reinforcing plate portion to reduce the weight of the plate may have any shape such as rectangular, circular or the like. Furthermore, the reinforcing plate may have larger wall thickness in a portion of the plate requiring strength, and a smaller wall thickness in another portion of the plate requiring less strength.
The punched windows may be disposed in any of a variety of arrangements, for example, a staggered arrangement, provided that the windows are distributed along the longitudinal direction of the guide.
The sliding contact guide in accordance with the invention, having the above-described configuration, produces the following beneficial effects.
First, the sliding contact guide imparts appropriate tension to a traveling, flexible transmission medium disposed in an endless loop, such as a chain, belt or the like, and suppresses both vibrations in the plane of travel of the medium (usually vertical and therefore referred to as xe2x80x9cvertical vibrationsxe2x80x9d), and transverse vibrations.
Further, since the reinforcing plate is provided with punched windows, which are open in the direction of the plate thickness, and distributed in the longitudinal direction of the guide, a significant weight reduction is achieved, and consequently the vibration energy of the guide, generated as a result of vertical vibration and transverse vibration of the flexible transmission medium, are reduced.
Since a through hole, provided in the plate at least at one end portion thereof, is fastened on a mounting bolt, pin, or the like, together with the body mounting hole of the guide body 10, vibrations between the guide body and the reinforcing plate, generated due to the traveling of the flexible power transmission medium, are also suppressed.
An example of a preferred embodiment of a sliding contact guide for a transmission device according to the invention will be described below with reference to the drawings.